The unique capability of molecular sieves for selective adsorption over a wide temperature range, particularly lend them for use in compressed gas filter units, where, because of the greater surface exposure to the gas, they are more effective in bead or other fine particle than in solid form. The drawback to the use of molecular sieve or other particulate desiccants in such filter units is that the particles, under flow of the compressed gas therethrough, abrade or rub against each other and produce dust, which, picked up by the gas, can detrimentally affect air brakes or other gas-operated devices when the product gas is so employed. At protracted intervals the particulate desiccant must be replaced and, to facilitate replacement, customarily is removably inserted in the housing of the filter unit. Heretofore, as disclosed in Hankison et al U.S. Pat. Nos. 3,464,186 and 3,572,008 and the copending application of Virgil L. Frantz, Ser. No. 569,812, filed Apr. 21, 1975, dust-producing abrasion has been mitigated against by compacting the particles by a coil spring either precompressed or, as in Frantz, compressed by the insertion of the canister. In either case, the effective compacting force of the spring is initially limited by the resistance practically imposable on loading or insertion of the canister and is reduced as the particles settle. It is with these problems that the present invention is particularly concerned.